This research deals with the manner in which nervous connections to muscle influence the selective gene expression in the latter which constitutes specialized fiber differentiation. Current research trends emphasize that imitation of the impulse pattern, which is natural for a slow muscle, changes a fast muscle into a slow one. We object that this result depends on a gross exaggeration of the impulse traffic. In contrast, we have developed a chronic animal preparation in which the spinal cord is deprived of all imputs and hence the motor neurons are silent. Thus, the muscles receive no stimuli, but are still attached to vegetatively intact though inert motor neurons. Muscle characteristics remain maintained in this preparation, and some become modified. In further research, we plan to investigate to what degree the neural influence upon specific muscle differentiation is still present in this situation, inasmuch as this would show it to be of nonexcitatory influence, and presumably involve formative substances acting, directly or indirectly, upon the genetic information.